If you have not already installed Magic Mirror as your current screensaver, do so. Right-click anywhere on the screem to bring up Windows Display Properties, select the screensaver tab, select Magic Mirror, then press the 'Apply' button.
The screensaver will now operate with its default options, which may be all you want. To control how it operates in more detail, press the 'Settings' button.
By default it plays 'wind-chime' sounds when it's running. Press the 'Sounds' button and select what options you want here.
By default, a new starting image will be loaded every 30 seconds - change the figure in the 'Reset time' box to alter this. [See also 'Show Source Picture' option.]
On the right of 'Reflections' is a checkbox saying 'Random'. If this is checked (recommended) the kaleidoscope will use a random amount of reflections in screensaver mode.
To help see what everything else does, check 'Split Screen'. That will show the original picture as well as the kaleidoscope image. Now press 'Detach' and stretch it so you can see better.
Unless you've sent movement to manual, the mirrors will be wandering across the source picture in one of a number of alternative modes. Try them, and select your favourite or else 'Random'.
You can tweak the magnification and the mirror movement speed. Just pick a level you like, or leave them about halfway, which is the default. [Higher magnification means the mirrors are smaller, and show a smaller part of the source picture. One effect of this is that you will see the original square pixels magnified.]
There's a button called 'Special' with a couple of extra options. One is the option to use only the last loaded image in screensaver mode (not recommended as a rule) . The other controls how often the 3-Mirror mode, which tiles the screen with multiple reflected images, comes up.